The 2-alkyl-2-cycloalken-1-ones are useful substances as an intermediate product for synthesis of physiologically active substances or perfume materials. Hitherto, the 2-alkyl-2-cycloalken-1-ones have been produced by first subjecting 2-(1-hydroxyalkyl)cycloalkanones to dehydration reaction to synthesize 2-(alkylidene)cycloalkanones, and then subjecting the 2-(alkylidene)cycloalkanones to isomerization reaction.
It is generally known that the above dehydration reaction is carried out in the presence of an acid. For example, Patent Documents 1 and 2 disclose the dehydration reaction using oxalic acid or phosphoric acid. Also, Patent Document 3 discloses the dehydration reaction using a solid acid.
On the other hand, there has been reported an example of the isomerization reaction using a metal catalyst. For example, Patent Document 4 discloses the isomerization reaction using a platinum group metal catalyst.
In addition, there is known the method in which the dehydration reaction and isomerization reaction are carried out only in one step. For example, Patent Document 1 discloses the method in which the dehydration reaction and isomerization reaction are carried out in one step under n-butanol reflux condition using hydrogen chloride or hydrogen bromide. Patent Document 5 discloses the method in which the reactions are carried out using hydrogen halides or sulfonic acids in the presence of an inert solvent while removing water out of the reaction system. Patent Document 6 discloses the method in which the reactions are carried out using sulfonic acids in the presence of a high-boiling solvent while removing water and 2-alkyl-2-cyclopentenone out of the reaction system.
The dehydration reaction and the isomerization reaction may be carried out separately from each other. In this case, the dehydration reaction may proceed in the presence of an acid as described in Patent Documents 1 to 3, whereas the isomerization reaction may proceed in the presence of a metal catalyst as described in Patent Document 4. However, when conducting these reactions separately, such a process tends to not only need an increased number of steps, but also become unsatisfactory in yield of the aimed product.
In the methods as described in Patent Documents 1, 5 and 6 in which the dehydration reaction and isomerization reaction are carried out in one step using an acid, the acid usable in these reactions is limited to a strong acid having a high corrosiveness against a reaction vessel used therein. As a result, in these methods, production facilities used therein are required to have a corrosion resistance. Further, 2-(alkylidene)cycloalkanones as the reaction intermediate product or 2-alkyl-2-cycloalken-1-ones as the reaction product tend to be susceptible to polymerization or decomposition, which will inevitably result in poor yield of the aimed reaction product. In addition, there tends to occur such a problem that a large amount of waste water is by-produced owing to neutralization, water-washing treatment, etc., after completion of the reactions.    Patent Document 1: JP-A 56-147740    Patent Document 2: JP-A 2004-217620    Patent Document 3: JP-A 2004-203844    Patent Document 4: JP-B 58-42175    Patent Document 5; JP-A 5-92934    Patent Document 6: JP-A 2001-261608